Reverse percentages start from the result rather than the total. If 72 is 80% of an amount, 72 represents 0.80 of the whole. Divide 72 by 0.80 and the whole is 90.
The formula
Whole = known part ÷ (percentage ÷ 100). The conversion from 80% to 0.80 is essential. Dividing by 80 instead of 0.80 changes the meaning of the answer.
A sale-price example
If an item costs €72 after 20% off, the sale price is 80% of the original. Divide €72 by 0.80 to get an implied original price of €90. This verifies the arithmetic but does not prove that €90 was a fair comparison price.
Common mistake
Do not subtract the percentage from the final price. Work out what fraction of the original remains, then divide by that fraction. Use the reverse percentage calculator to show the steps.
Use the related calculator, then read our methodology, sources, and editorial policy. Spot an error? Contact the site.